1. Field of the Invention
The present invention relates generally to a method and device to treat and remediate contaminated soils and sludges and, in particular, relates to a treatment unit which is transportable, quickly mobilized, and capable of remediating large quantities of waste by exothermic stabilization processes such as the calcium oxide based DCR process.
2. Description of Related Art
The present invention is a Transportable Treatment Unit (TTU) designed to efficiently treat large volumes of heavily contaminated soils and sludges using exothermic stabilization processes, such as the calcium oxide based Dispersion by Chemical Reaction (DCR) process. The DCR process is an adsorptive process utilizing the increasing specific surface area available for adsorption during calcium oxide hydration reactions. DCR has applications for the stabilization of organic wastes, or mixtures of inorganic materials and hydrocarbons. In general, the oil is carried through the exothermic hydration reaction and is adsorbed homogeneously throughout the hydroxide. The oil is eliminated from the oily phase by virtue of being adsorbed onto the hydroxide in molecular thicknesses across a dramatically increased surface area. Specifically, DCR utilizes certain chemical compounds such as quicklime which, upon reacting with water, form solids wherein the specific surface area increases dramatically, over 30-fold, in what is termed a dispersing reaction. The DCR process, and some laboratory approaches used to predistribute the material, are described in U.S. Pat. Nos. 4,018,679, 4,350,598, and 4,448,971.
With a DCR process, oils and oily substances are converted from mobile liquid materials into pulverulent materials by taking advantage of these dispersing reactions. However, this is only possible by evenly predistributing the oily material in the quicklime prior to affecting the hydration reaction. The predistribution has not been achievable on a large and efficient scale to date.
In the prior art, the majority of treatment units used for waste stabilization are flow through pug mills. However, there is a number of deficiencies and problems in the prior art for waste stabilization. Pug mill units provide for mixing in low RPM (&lt;40 rpm) pug mill mixers where waste, reagent, and water are loaded in one end of the mixer and discharged through the other after mixing for 10 to 40 seconds. These systems work well when mixing granular soils with cement reagents. However, these systems do not work well when mixing cohesive materials such as tarry contaminated wastes or clay contaminated matrices.
The minimal mixer residence time and low mixer rpm frequently result in poor mixing using these systems. In addition, the flow through system requires all mix components be added in the load end of the mixer and does not provide for waste conditioning or premixing with water prior to addition of reagent. This flow through system also does not provide for much flexibility in extending mix times, as may be required to treat certain cohesive wastes.
Further, pug mill systems used in the waste treatment industry are open systems and do not provide for dust and/or volatile emissions containment. These systems are particularly poorly suited for treatment processes involving exothermic hydration reactions, such as calcium oxide-based processes. These processes rapidly heat treated waste and evolve volatile emissions. Frequently, alternative and more expensive treatment processes are chosen over calcium oxide-based processes because available treatment equipment lacks emissions containment systems.
Another problem with most pug mill systems is that they are fed by belt feeders with shear gate modulating systems. These systems are frequently blocked by debris in waste. Also, these systems frequently pass rock, concrete, and metal debris into mixers that can damage mixer components.
Another problem area with the prior art is that standard weigh batch hoppers receive both reagent and waste. This allows interaction between waste and reagent prior to discharge into mixers. This is a problem with highly reactive reagents, such as calcium oxide. Interaction between waste and reagent prior to mixing can result in wasted reagent with these systems.
Standard hopper systems only provide for simultaneous discharge of waste and reagent into mixers, preventing any preconditioning of waste in mixer prior to discharge of reagent.
Still another disadvantage associated with the prior art system is the use of a single mixer system. Single mixer systems, batch and continuous, suffer total shutdown when mixer operation is interrupted for maintenance or repair. This negatively impacts system economics because all treatment operations must cease until equipment is returned to operation. Dual train operation provides for continued treatment on one mixer system, while repairs are made to the other. This provides for continued utilization of project assets while repairs are made or maintenance is performed.
Generally batch treatment can provide for user control of the mixing cycle (i.e., mix time, waste conditioning with water prior to reagent addition, sequential addition of reagent and water, etc.). However, attempts to utilize a batch treatment program with the prior art single mixer system generally have reduced overall waste treatment rates due to extended cycle times.